Benchmark: timing 10000 iterations of beatnik1, chipmunk1, chipmunk2
  beatnik1: 536 wallclock secs (449.49 usr +  2.70 sys = 452.19 CPU)
 chipmunk1: 390 wallclock secs (360.76 usr +  2.25 sys = 363.01 CPU)
 chipmunk2: 313 wallclock secs (250.84 usr +  2.00 sys = 252.84 CPU)